To clean the wall surfaces of a tank or vessel, a number of different rotating nozzle designs have been used. Most of these designs are very similar in construction, and typically include a rotor with one or more nozzle ports or orifices which are supplied with water under high pressure. The nozzle ports are skewed with respect to the axis of rotation at some selected angle to provide a reactive torque which causes the nozzle to spin in operation. High pressure water is transferred to the nozzle by a tubular body having a threaded connection at one end and a long hollow shaft extending from the other end thereof. A tubular bushing provides a rotational interface between the body, which is stationary, and the rotating nozzle. In an effort to prevent leakage, the bushing is machined with tight clearances and typically is pressed into the rotor but slides on the shaft. In many cases an aligned set of holes in the bushing and the shaft transfer high pressure water from the body to the spinning rotor.
A rotating or spinning nozzle provides increased cleaning area coverage as compared to a conventional straight or fanned tip nozzle in a pressure range of from 1000 to 50,000 psi. By covering more area, cleaning times can be reduced to save on cleaning costs. Shortened cleaning time has the additional benefit of reducing wear time on the waterblast components such as the pump and the cleaning gun parts. This reduces the operating costs.
Examples of prior rotating waterblast nozzle assemblies are shown in U.S. Pat. No. 4,821,961, and in the advertising materials of the Hammelmann Corp. dated Oct. 26, 1987 for its so-called "Rotorjet" nozzle. These devices have a similar construction but somewhat different operating characteristics such as rotor speed and flow and pressure requirements. However, these devices are considered to be exemplary of prior devices in the technology to which the present invention relates. These nozzles have very small machining tolerances and very tight clearances, and thus have relatively low reliability when they are subjected to dirty or gritty water, or rough handling or other improper use. Such tolerance and clearances are necessary to prevent excessive leakage or "wasted" water. Any leakage represents essentially lost horsepower that must be paid for with increased fuel or electricity usage at the waterblast pump. To make matters even worse, the amount of leakage or leakby is generally proportional to the operating pressure and becomes worse as the tightly clearanced parts wear in use. When a certain degree of wear occurs the components must be replaced. However in most cases these component parts cannot be easily replaced in the field and generally the assembly must be returned to the manufacturer for a lengthy and costly repair.
An object of the present invention is to provide a new and improved rotating nozzle assembly for high pressure waterblast cleaning that is constructed and arranged to obviate the foregoing problems.
Another object of the present invention is to provide a new and improved rotating nozzle of the type described having reduced clearances under higher pressure to minimize leakby.
Still another object of the present invention is to provide a new and improved nozzle assembly of the type described which is simple in construction, more efficient in operation, and easier and more economical to maintain and operate than prior devices.